Chronic back problems are caused by intervertebral disc disease and deterioration and loss of stability of the intervertebral joints. Examples of these spinal conditions include degenerative disc disease, scoliosis, spondylolisthesis, spinal stenosis, etc. Stabilization and/or arthrodesis of the intervertebral joint can reduce the pain associated with movement of a diseased or deteriorated intervertebral joint. In order to allow for development of a solid intervertebral fusion, the spine has to be stabilized. Severe trauma to the back can further cause conditions wherein the spine needs to be stabilized. There are many instances in which it is necessary to stabilize and fix bones and bone fragments in a particular spatial relationship to correct the location of skeletal components due to injury or disease. One group of devices employ a number of bone screws placed across a discontinuity in adjacent vertebrae and connected by a rod to maintain a predetermined spatial location.
Spinal stabilization systems have been developed to stabilize the vertebrae to allow for fusion or stabilization of diseased intervertebral joints. One type of spinal stabilization system includes connectors and rods that are used to stabilize the spine. Some examples of such spinal stabilization systems are disclosed in U.S. Pat. Nos. 6,613,050; 6,371,957; 6,050,997; 5,879,350; 5,725,527; 5,628,740; and 5,545,165, the disclosures of which are incorporated herein by reference. In these systems, connectors are anchored to the vertebral bodies desired to be stabilized by anchoring structures such as screws or hooks. One or more connecting rods are then secured to the connectors to form a connector/rod construct that stabilizes the vertebral bodies to which the connectors are secured.
The inventors implants includes U.S. Pat. Nos. 7,105,029; 7,118,303; 7,334,961; 7,335,201; 7,438,715; 7,658,582; 7,678,138; 7,862,281; 7,981,143 and RE42,715, the disclosures of which are incorporated herein by reference. In normal practice a screw and modular head are assembled in a factory before being anchored to a bone. Alternatively a screw is anchored to the bone and the modular head then secured to the screw. The modular heads, which are commonly referred to as a tulip, are then connected together by a rod having sufficient stiffness to maintain the desired skeletal orientation. The problem with mounting a tulip onto a bone screw is the pressure necessary during the installation step. Thus, what is needed in the art is an instrument to mount a tulip to an anchored bone screw wherein the instrument has a force canceling effect.